GRC (GFRC) Panels — Facade Cladding, Jaalis and Mouldings

What it is

Glass-fibre reinforced concrete (GRC, or GFRC) is a cement-rich sand mortar reinforced with alkali-resistant (AR) glass fibre and cast thin, usually as facade panels, perforated jaali screens, cornices, column covers and mouldings. The AR fibre carries tension that plain mortar cannot, which is what allows a section thin enough to look like carved stone while weighing a fraction of it.

What the choice turns on commercially is the cost of a cracked panel. Each GRC element is cast to a project-specific mould, so a cracked panel has to be recast, often from a scrapped mould, and replaced from a scaffold. Nearly every cause of that failure is decided at design and fixing-detail stage.

GRC types and where each is used

Weight, fixings and movement

GRC is specified for its low weight relative to precast concrete and stone: lighter support steel and fewer heavy lifts, which matters most on retrofit facades and upper floors with limited crane access.

The material moves throughout its life. It shrinks as it dries after casting and then expands and contracts with temperature and moisture. A well-detailed panel is fixed so that it is held, not clamped:

• One or two fixings carry the weight; the rest restrain wind load only and allow movement in the plane of the panel
• Stud-frame panels use flexible anchors between the skin and the frame, so the frame does not fight the skin as it shrinks
• Open or sealed joints between panels are sized for movement, as for any facade movement joint; GRC must never be butted hard against the structure or the next panel
• Fixings are corrosion resistant, because a fixing that rusts inside a thin section bursts the concrete around it

The wind load each panel and fixing must resist is set by the structural engineer for that building under IS 875 (Part 3). Panel size, anchor spacing and frame design follow from that calculation and from the manufacturer's tested material properties, never from an elevation drawing.

Curing and quality control

GRC is cement-rich and thin, so it dries fast and shrinks more than ordinary concrete. Panels need controlled curing after demoulding, either by keeping them moist for the period the producer's method states or by an approved curing admixture in the mix. Panels rushed out of the yard green are the ones that craze and crack within the first year.

EN 1169 sets out factory production control for GRC: raw materials, mixing, and checks on fresh and hardened material. EN 1170 gives the test methods, including fibre content, bending strength, water absorption and density. EN 15191 classifies GRC performance for design. Asking a producer which of these they test to, and how often, quickly shows how controlled the factory is.

For larger feature work, a building-level view of architectural facade elements covers how GRC sits alongside fins, canopies and screens.

Where GRC fails

• Restrained movement. Too many rigid fixings, or panels grouted tight to the structure. Cracks appear at corners, openings and fixing points.
• Poor fixings. Anchors cast too close to an edge, ferrous fixings that corrode, or a frame that deflects more than the skin can follow.
• Inadequate curing. Surface crazing and shrinkage cracks, especially on panels cast and despatched in hot, dry weather.
• Efflorescence. White salt staining as water moves through the cement, most visible on dark pigmented GRC. Breathable sealers and drainage reduce it.
• Water trapped behind panels. Without drainage paths and a ventilated cavity, water sits against fixings and the back face. The principles are the same as for other facade cladding systems.

Common mistakes

• Choosing GRC by render, then designing fixings later. The fixing and movement concept should be agreed before the panel geometry is frozen.
• Too many unique shapes. Each distinct profile needs its own mould. A facade rationalised to a small set of repeated moulds is faster and cheaper to make, and easier to replace.
• No spare panels or retained moulds. Order a small stock of spares for exposed jaalis and keep the master moulds until the defects period ends.
• Thin jaali webs drawn for appearance. The narrowest bars between openings must suit premix casting and handling, or they break in transit.
• Sealing a joint that was meant to move. A rigid mortar joint between panels transfers stress straight into the GRC.
• Comparing GRC with stone or terracotta cladding on panel price alone. The support steel, lifting and replacement risk change the comparison.

What to ask your contractor or supplier

• Is this sprayed or premix GRC, and what fibre content is targeted?
• Which tests under EN 1170 do you run, and how often, on this production?
• How is each panel fixed: which fixings carry weight and which allow movement?
• What curing regime do you use, and for how long before despatch?
• What are the joint widths, and how is water drained from behind the panels?
• How many moulds does this design need, and will they be retained?

Standards referenced

Production control of GRC under EN 1169, performance classification under EN 15191, and test methods under EN 1170. Glass fibres for mortar and concrete reinforcement under EN 15422, and alkali-resistant glass fibre for GFRC under ASTM C1666/C1666M. Wind loads on cladding and its supports under IS 875 (Part 3). Panel sizes, fixing design and wind loading for a specific building must be confirmed by the project's structural and facade engineers.